/Engine/Source/Runtime/UMG/Public/Components/WidgetInteractionComponent.h
Releases a key as if the mouse/pointer were the source of it. Normally you would just use Left/Right mouse button for the Key. However - advanced uses could also be imagined where you send other keys to signal widgets to take special actions if they're under the cursor.
virtual void ReleasePointerKey ( [FKey](API\Runtime\InputCore\FKey) Key )